Because pitot static probes for measuring aircraft speed and altitude are delicate instruments, they are generally covered before installation. Moreover, when an aircraft is on the ground for an appreciable time, pitot covers are temporarily installed to prevent introduction of foreign matter into the probes. Pitot covers must be removed before flight for the pitot-static system to operate properly.
Commercial aircraft are generally provided with means to heat pitot static probes to prevent ice formation inside the pitot tube or at the static ports. There have been occasions when covers have inadvertently been left in place and pitot heat has been applied. Before this invention, considerable damage could be done to the pitot tube by the melting or burning of the cover material.
A number of different approaches were taken to solve this problem. A ceramic material was formed to cover the pitot tube probe tip, the static ports, and the aft region of the tube with openings between these three areas for heat dissipation. The ceramic material was supported with a steel frame. After about three hours of pitot heater operation, the ceramic material darkened over most of the visible regions. The ceramic material also began to fray and left fiber-like residue on the pitot probe when the cover was removed. This lead to concern that dirt or contamination could be trapped between the cover and the pitot tube. There were further concerns about moisture or dirt being introduced into the pitot tube if the cover should become dirty.
Another pitot cover was designed using gray E-glass material with an aluminum outer shell in a sock-style configuration. The material was soft enough to properly protect the probe, but the aluminum shell caused an oven effect in still-air operation and the pitot probe became too hot. The cover also left a gray residue, and the aluminum outer shell became very embrittled when exposed to pitot heat.
Another sock-style cover was made from E-glass with a stainless steel wire intermesh. After heater operation with the cover installed, the cover turned mostly brown and the temperature of the pitot probe rose unsatisfactorily. The steel wire intermesh was considered unacceptable because it scratched the nickel plating on the pitot tube.
Accordingly, an improved pitot cover was invented in accordance with this invention.